Motor-control system



L. MILLER AND W. BROOKE.

MOTOR CONTROL SYSTEM.

APPLICATION FILED NOV. 26. 1919,

I Patented Mar. 23, 20.

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INVENTORS Lap/2am Mil/er WITNESSES:

ATTORNEY L. MILLER AND W. BROOKE.

MOTOR CONTROL SYSTEM.

APPLICATION FILED NOV. 26. 1919.

1,334,9 1 9. Patented Mar. 23, 1920.

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WITNESSES: INVENTOR-S Leonard Mil/er Wf/fr/d Brae/re.

UNITED STATES PATENT OFFICE.

LEONARD MILLER, OF WHITEFIELD, AND WILFRID BROOKE, OF ALTRINCHAM, ENGLAND, ASSIGNORS TO WESTINGHOUSE ELECTRIC & MANUFACTUBING COMPANY, A CORPORATION or PENNSYLVANIA.

MOTOR-CONTROL SYSTEM.

Specification of Letters Patent.

Application filed November 26, 1919. Serial No. 340,899.

To all whom it may concern:

Be it known that we, LEONARD l IILLnn, a subject of the King of Great Britain, and a resident of Whitefield, in the county of Lancaster, England, and WILFRID BROOKE, a subject of the King of Great Britain, and

a resident of Altrincham, in the county of system of the above-indicated character which shall be adapted for automatically shunting, or otherwlse rendering lneffectlve, portions of the starting resistor 1n accordance with current conditions obtaining in the motor circuit.

Our invention is a modification of, and an improvement upon the system of control shown and described in the co-pending application vof Leonard Miller, Serial No. 295,187, filed May 6, 1919, motor control systems, and assigned to the WVestinghouse Electric & Manufacturing Company.

According to our invention, each of a series of successively operable switches for controlling the starting resistor is controlled by a relay that is adapted to close when the current traversing the motor circuit falls to a predetermined value. Each of the relays is provided with an actuating coil having a number of turns in excess of that necessary for normal operation. The excess turns of each of the relays are shunted by the switch controlled by the relay previously closed.

By means of our improved arrangement, all of the relays are maintained intheir open positions during the acceleration of the motor, even though the current falls below the predetermined value for which they are adjusted to operate, until the switch controlled by the preceding relay has been closed to shunt the corresponding section of the startingresistor and to shunt the excess turns of the relay for controlling the succeeding switch. This arrangement insures, also, that the relay's c10se* in sequence a'nd only upon the current falling successively to the predetermined value at which the sections of the starting resistor are to be removed from circuit.

In the accompanying drawings, Figure 1 is a diagrammatic view of a direct-current system embodying our invention. Fig. 2 is a view, similar to Fig. 1, of a system ar ranged for operation in connection with a source of alternating current.

Referring to Fig. 1, the armature 1 of a direct-current electric motor has a series field-magnet winding 2. A starting resistor, having sections 3, 4, 5 and 6, is in series with the motor armature and the field-magnet winding. The motor is supplied with energy through line conductors 7 and 8 which maybe connected to any suitable source of direct-current. The direction of rotation of the motor is controlled by pairs of switches 9 and 10 having actuating coils 11 and 12, respectively, and switches 13 and 14 having actuating coils 15 and 16, respectively.

The resistor sections 3, 4, 5 and 6 are controlled by switches 17, 18, 19 and 20. that are respectively provided with actuating? coils 21, 22, 23 and 24. The circuits of the coils 21 to 24 are controlled by relays 25, 26, 27 and 28, respectively. A master controller 29, which is illustrated as being of the usual drum type, controls the operation of the reversing switches and the control circuits of the system. The relays 25 to 28 are provided with actuating coils '30, 31, 32 and 33, respectively, that are in series with the motor. The sections 34, 35 and 36 of coils 31, 32 and 33, respectively, are so arranged that they are shunted upon the operation of switches 17, 18 and 19, respectively. The relay 25 is provided with a second actuating coil 37 having a shunt-circuit which includes interlocks 38 and 39 and a no-voltage relay 40. The coil 37 maintains the relay 25 and connected switches 44, 45 and 46 in their open positions when the controller is in its off position.

The interlocks 38 and 39 are respectively closed when the switches 9 and 13 are in their open positions. It will be noted that the circuit of the coil 37 is open when either of the pairs of reversing switches are closed or upon the opening of the no-voltage relay 40 because of a failure of voltage across the terminals of its actuating coil 41.

Patented Mar. 23, 1920.

The circuit of the coil 41 of no-voltage relay 40 is controlled by an overload relay 42 having a series actuating coil 43. The circuits of the actuating coils of the switches 18, 19 and 20 are respectively controlled also by switches 44, 45 and 46 that are mechanically connected to the relay 25 for simultaneous operation therewith. This arrangement provides that the switches for controlling the sections of the resistor cannot operate when the relay 25 is open, regardless of the positions of their corresponding con trolling relays and of the value of the current traversing the motor circuit.

It may be assumed that the several switches and controller 29 occupy their respective illustrated positions and that the line conductors 7 and 8 are connected to a source of energy. The coil 41 of the no voltage relay is energized by a circuit which extends from line conductor 7 through conductor 47, contact member 48, conductor 49, coil 41 and overload relay 42 to line conductor 8. A second circuit extends from line conductor 7 through no-voltage relay 40, interlocks 38 and 39, and coil 37, to line conductor 8.

To start the motor in the forward direction, the controller 29 is actuated to theleft from its 0135' or illustrated position. A circuit is completed which extends from line conductor 7 to conductor 47, contact member 48, contact members 50 of the controller drum, contact member 51, conductor 52, coils 11 and 12 of reversing switches 9 and 10, and conductor 53 to line conductor 8. The switches 9 and 10 then close to complete the main circuit of the motor which includes series field-magnet winding 2, the several resistor sections 3, 4, 5 and 6, coils 30 to 33, inclusive, and coil 43 ct overload relay 42. The relays 26 to 28 are actuated to their open positions because of? the relatively high value of the current traversing the motor circuit. 7

The closing of switch 9 opens the circuit of the coil 37 and the latter is deenergized, the series coil 30 controlling the operation of the relay 25. When the value of the current in the main motor circuit has fallen to the predetermined value, the relay 25 closes, but the coils 31, 32 and 33 maintain the re lays 26, 27 and 28 in their open positions because Of the excess turns included in circuit. The closure of relay 25 completes a circuit which extends from contact member 48 of the controller, through contact members 50 and 53 conductor 54, relay 25 and coil 21 to line conductor 8. The switch 17 then closes to complete a shunt circuit for re sistor section 3, series coil 30 and section 34 of coil 31.

The shunting of resistor section 3 causes a temporary increase in the value of the current traversing the motor circuit. When the motor has accelerated sufficiently, the current again falls to the predetermined normal value. The coil 31 permits the relay 26 to close and thereby complete a circuit which extends from contact member 48 through contact members 50 and 53,, conductor 54, relay 26, conductor 55, contact members 56, 57, 58 and 59, conductor 60, relay 44 and coil 22 to line conductor 8. The switch 18 then closes to complete a shunt circuit for section 4 ot the starting resistor, this circuit including also section 35 of coil 32.

When the current traversing the motor circuit falls to the predetermined value, the relay 27 closes in the manner previously described in connection with relays 25 and 26 to effect the closing of switch 19. The closing of switch 20, which completes a shunt circuit for the entire resistor and also the respective coils of the relays 25 to 28, is effected in the same manner as that described above.

It will be observed that the sequence of operation above described may be controlled within certain limits by the manipulation of the controller. For example, if the latter is moved to its first operative position, the contact member 53, will not engage the corresponding contact member 50, and coil 21 cannot be energized until its circuit is completed by these contact members. Similarly, the engagement of contact members 56 and 57 is necessary for the completion of the circuit of coil 22 of switch 18.

In order to obtain the reverse direction of rotation of the motor, the master con troller is moved to the right, as viewed in Fig. 1, to effect the engagement of the contact members 50 and 57 with the corresponding contact fingers. In this position of the controller, the coils 15 and 16 oi reversing switches 13 and 14 are energized to complete the main circuit of the motor with the connections 01" the armature 1 reversed relatively to that previously de scribed. Since the operation of the several relays and switches is similar in every respect to that previously described, a detailed description thereof is unnecessary.

Fig. 2 is a diagrammatic view showing a system substantially like that of Fig. 1 but applied to a three-phase alternating-current motor. The alterations which are thereby rendered necessary Will be readily understood from the drawing. Line conductors 71, 72 and 73, which may be connected to any suitable source of alternating current, supply energy to an alternating-current motor 74, the rotor of which is provided with slip rings 75, 76 and 77 connected to resistors 78, 79 and 80, respectively. Instead of employing a single overload relay, as in the system of Fig. 1, three overload relays 90, 91 and 92 are provided, the relays having actuating coils 93, 9a and 95 that are in circuit with the respective resistors.

The shunt coil 37 of the relay 25 is in circuit with the contact members 38 and 39 which are respectively interlocked with reversing switches 9 and 10, and 13 and 1a. In the present arrangement, switches 9 and 10 are mechanically connected and con trolled by a single actuating coil 96. Switches 13 and 14, which are similarly connected, are provided with an actuating coil The sections of the several resistors are controlled by pairs of switches 98 and 99, 100 and 101, 102 and 103, 10a and 105 which are respectively actuated by coils 21 to 2%. The several pairs of switches correspond to the switches 17 to 20, inclusive, of the system of Fig. 1.

It will be readily observed that the electrical connections of the various switches, actuating coils and relays for the controller 29 are substantially the same as those shown in Fig. 1, and a description of the operation of that figure will apply to the system of Fig. 2, taking into account the alterations hereinbe'fore referred to, and will readily be understood by those skilled in the art without further description.

We claim as our invention.

1. In a motor-control system, the combination with an electric motor and a resistor in circuit therewith, of a plurality of successively operable switches for controlling said resistor, said switches being normally in open positions, and a relay operable independently of said switches for controlling the operation of one of said switches in accordance with the value of the current traversing the circuit of said motor, said relay having a coil, a portion of which is shunted by the switch PIGCGCllIlg' that controlled by the relay, said relay being operable to effect the opening of the switch controlled by it when the current exceeds a predetermined value.

2. In a motor-control system, the combination with an electric motor and a resistor in circuit therewith, of a plurality of normally open switches for controlling said resistor, and a plurality of relays mechanically independent of said switches for controlling the operation of said switches, each of said relays having a coil tending to maintain it in its open position, each of said relay coils except that for the first relay to clos having a portion included in a shunt circuit controlled by one of said switches, and each of said relays being operable to effect the opening of the switch controlled by it when the current traversing the motor circuit exceeds a predetermined value.

3. In a motor-control system, the combination with an electric motor, and a resistor in circuit therewith, of a plurality of normally open switches for controlling said resistor, each of said switches having an actuating coil, and a relay mechanically independent of said switches for controlling the circuit of ach actuating coil, one of said relays having an actuating coil controlled by one of said switches, whereby said relay is maintained in open position when the current traversing its actuating coil exceeds a predetermined value and, upon the closing of said switch, said relay is closed when the current is below a second and higher predetermined value, said relay being operable to effect the deenergization of the corresponding switch-actuating coil when the current exceeds the second value.

4. In a motor-controlled system the combination with an electric motor and a resistor in circuit therewith, of a plurality of normally open switches for controlling said resistor, and means for insuring the operation of said switches in a definite sequence and at a predetermined value of the current traversing the circuit of said motor, said means comprising a series of relays mechanically independent of said switches having coils for maintaining them in open position when the current traversing the motor circuit is above a second and lower predetermined value and for permitting each of them to close at the first predetermined value when the preceding relay and the corresponding switch are closed, said relays being effective to open the circuits of the actuating coils of the corresponding switches when the current again exceeds the first predetermined value.

In testimony whereof we have hereunto subscribed our names this 16th day of September, 1919.

LEONARD MILLER. WILFRID BROOKE. 

